Diagnostic Trouble Code (DTC) P0172

Fuel Trim System Too Rich

 

Circuit Details

 

  • In this circuit a Closed Loop air/fuel metering system is used for getting the best of  driveability, fuel economy, and emission.
  •  The Engine Control Module (ECM) ,even when it stays in a Closed Loop checks the Front Heated Oxygen Sensor (HO2S1) signal voltage and regulates the delivery of fuel depending on the signal voltage.
  •  If there is any variation in the fuel delivery it will be highlighted by the long and short term fuel trim values
  • These values are checked by the scan tool.
  • NOTE: The best fuel trim values dwell around 128 (0%).
  •  If a lean condition is signaled by the HO2S1 then the ECM will add fuel to the extent that the fuel trim values go beyond 128 (0% to 100%).
  •  If a rich condition is signaled then the fuel trim values will be found to dip to 128 (0% to -100%), which means that the ECM is lowering the quantity of fuel being supplied.
  • In case the exhaust emissions fluctuate to abnormal levels because of either a lean or rich condition, a fuel trim Diagnostic Trouble Code (DTC) will be boosted.

 

 

 

When will DTC set?

 

Task boosted after DTC sets

When will DTC clear?

DTC sets when

1) The average of short term fuel trim value > or = 1.06.

1) The Malfunction Indicator Lamp (MIL) will be seen to glow after two successive ignition cycles in which the diagnostic runs with the fault active (SOHC).

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1) The MIL will go off after four consecutive ignition cycles where the diagnostic is found running faultlessly.

 

2) No intrusive tests show that it is active.

2) The Malfunction Indicator Lamp (MIL) will also be seen after first repetitive ignition cycle (DOHC).

2) A history DTC will automatically clear after 40 consecutive warm-up cycles faultlessly.

3) Throttle Position (TP) < 80%.

3) This information will be stored in the Freeze Frame and Failure Records will be boosted.

3) The Scan Tool can be used to unset all DTCs.

4) Engine speed ranges round 700 and 6000 rpm.

4) A history DTC is stored.

4)  If the ECM battery feed is de-linked for more than 10 seconds.

5)   Barometric Pressure (BARO) > 72.0 kPa (10.4 psi).

 

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6)  Coolant temperature dwells between 70 °C(158 °F) and 105 °C(221 °F).

 

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7) Manifold Absolute Pressure (MAP) dwells between 25 kPa (3.6 psi) and 90.0 kPa (13.1 psi).

 

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8) Intake Air Temperature (IAT) ranges round -10°C (14°F) and 90°C (194°F).

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9) Airflow revolves round 1.5 and 45 g/sec.

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10)  Vehicle speed < 140 km/h (87 mph).

 

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11) System is in closed loop.

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12) Adaptive index is ready.

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13)  System voltage > 11 volts.

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14) DTCs P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0131, P0132, P0133, P0134, P0135, P1167, P1171, P0300, P0336, P0337, P0341, P0342, P0402, P0404, P1404, P0405, P0406, P0443, P0506, and P0507 are not set.

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Diagnostic TOOLS

 

 

NOTE: After repairs, use the scan tool Fuel Trim Reset function to reset the long-term fuel trim to 128 (0%).

 

You need to check if there is any ill connection at the ECM. You must examine the harness connectors for the following conditions:

·   Backed-out terminals

·   Improper mating

·   Broken locks

·   Improperly formed

·   Damaged terminals

·   Poor terminal-to-wire connection

Probe the wiring harness to see if there is any error. If the harness seems to be perfect then see the HO2S1 reading on the scan tool as you move the connectors and the wiring harness related to the engine harness. A variation in the reading will indicate the source of the fault.

You may also examine the brake power booster and the valve for any possible leaks.

If you see that a DTC P1404 is also set then look up the 5 volt reference circuits to see if there exists any short to voltage. Also note if there is any restricted exhaust system.

A shorted 5 volt reference circuit may set a DTC P0172. Examine the 5 volt reference sensors for unusual readings.

 

 

 

 

Purpose of the test

 

Number(s) below refer to the step number(s) on the Diagnostic Table.

 

1.The On-Board Diagnostic (EOBD) System Check assists the technician to finish some routine checks and store the freeze frame and failure records data on the scan tool if applicable. An electronic copy of the data is obtained when the malfunction occurs and this data is then stored on the scan tool for future use.

5. In this step we check the condition of the air cleaner filter as a clogged air cleaner filter element may obstruct the airflow coming into the engine.

17.   A leaking injector may result in setting a rich condition thereby boosting DTC P0172. In this matter consult "Fuel Injector Balance Test" in this section.

19.   An ill fitted TP sensor may not set a TP sensor associated to any DTC, but may make the system rich by a higher-than-actual TP reading.